1. Technical Field
The invention generally relates to a method, system and device for obtaining data that can be used to detect ocular dysfunctions. More particularly, the invention provides a method, system and device for exposing one or both eyes to a series of light flashes and measuring the direct and/or consensual pupillary reflexes that can be used to detect the presence of various dysfunctions and/or disorders.
2. Background Art
During eye examinations, the pupillary reflexes of a patient are often monitored to determine the presence of various ocular dysfunctions. The presence of one or more ocular dysfunctions can signal that the patient suffers from an ocular disorder such as optic neuropathy, other pathology of the ocular pathways between the photoreceptors of the retina and brain, opacification of the ocular media, or conditions that impact the transmission of light through the ocular media. A common objective visual functional test for the detection of such visual dysfunctions is the “Swinging Flashlight Test” (SFT). For the SFT, a handheld, very bright light source is shined first into one eye of the patient and then into the other eye, in a pendular fashion with a period of one to two seconds. While this is being done, the examiner will observe the reflexes of the patient's pupils. A detection of a positive sign is made based on the observed reflexes.
For example, if the light is shined into an eye that has an optic nerve conduction defect, while the other eye does not, the pupil of the eye with the defect, will contract to a lesser degree than will the pupil of the eye without the defect when that eye is stimulated with the same light. Similarly, if both eyes have a defect, one having a greater defect than the other, the light being shined into the eye with the greater defective optic nerve will evoke a lesser pupillary contraction of both pupils than would the same light shown into the eye with the lesser optic nerve defect, thus yielding the sign of a Relative Afferent Pupillary Defect (RAPD). Moreover, in the presence of a RAPD, when the light is alternated every few seconds between the two eyes, these differences in pupillary reflexes to the same bright light shined into the two eyes may give rise to an “illusion” that shining the same bright light into the eye with the greater defect caused its pupil to dilate (or expand), a so called Marcus-Gunn pupil.
The SFT is a foremost example of an objective functional test of the visual system that depends upon differences in pupillary reflexes to infer the presence of an ocular dysfunction, and therefore an ocular disorder (i.e., disease or pathology). However, this test has numerous drawbacks. In particular, it lacks specificity for any one ocular disorder whether of neurological or transmissive origin. It can be positive in unilateral dense cataracts, in certain unilateral retinal disorders, in anisocoria, as well as in significant asymmetric glaucoma. The clinician can not tell which ocular disorder is present based on the pupillary reflexes alone. Moreover, the SFT lacks sensitivity due to the manner in which the differences between the direct and consensual reflexes are observed. For example, the clinician can not observe the pupils of both eyes simultaneously, but must visualize the reflex of one pupil first and then visualize the reflex of the other pupil moments later. As a result, small differences in reflexes may go unnoticed. The unaided observation makes this comparative judgement subject to significant error and makes the detection of small differences in reflexes between the two eyes especially problematic. Because the SFT relies on the examiner's naked eye to detect and diagnose ocular dysfunctions, it lacks practical utility. Moreover, by depending on a single bright light, the SFT stimulates the visual system in an indiscriminate manner. As a result, this manner of evoking the pupils' reflexes, has proven to be lacking in both sensitivity and specificity.
Further, several observations have been made concerning the ocular disorder glaucoma, thought to be a form of optic neuropathy. First, glaucoma and glaucoma suspect patients display a significant degree of dyschromatopsia, i.e., deficiencies in color discrimination. Second, patients with asymmetric glaucoma, as measured by visual field loss and cup-disc ratios, manifest gross afferent pupillary defects to a greater extent than do patients without glaucoma. Third, a consensual pupillary reflex can be induced by the interchange of equally luminous, heterochromatic members of a pair of monochromatic lights shined into the patient's contralateral eye. This finding must mean that chromatic differences in stimuli, activate pupillary reflexes via stimulation of different cell populations independently of the luminosity change that is thought to be the primary basis of the pupillary reflex activation in the SFT.
Although not previously brought to bear on detecting specific ocular dysfunctions, attempts have been made to solve these problems by implementing systems and devices for measuring pupillary reflexes to light stimuli. Such devices generally implement a system for exposing a patient's eyes to stimuli and then measuring the pupillary reaction thereof. In particular, the goal is to intentionally induce a pupillary reflex and then measure the reflex using various means. Since dimensional changes in the pupil's movements can often be minuscule, the comparison to a range of “normal” reactions obtained from different patients can lack accuracy. Without an appropriate validation procedure, this could lead to either a false diagnosis of a disorder that is not present, a failure to diagnose a disorder that is present, or a failure to distinguish between two ocular diseases. Furthermore, if the examiner is seeking specific information, for example, about the afferent optic nerve pathology of a patient, efferent deficiencies may significantly confound the interpretation of such sought for information.
Therefore there exists a need for a method and device that allow for the sensitive and accurate recordation and/or comparison of the pupillary reflexes of a patient's eyes to a series of flashes that target specific cell populations of the visual system. Moreover, there is a need for a method, system and device that are able to differentiate between various asymmetries of afferent or efferent origin, whether revealed in the afferent or the efferent branches of the pupillomotor system, and whether they be of retinal, ocular, illuminometric, or optic nerve origin.